A common spark plug for an internal combustion engine comprises a center electrode enclosed in an elongated ceramic body and an L-shaped side electrode attached to a metal shell crimped about the ceramic body. At the tip of the spark plug, the center electrode protrudes from the ceramic body and is spaced apart from the side electrode to form a spark gap. The metal shell includes screw threads to allow the spark plug to be installed in a cooperatively threaded bore of a cylinder head such that the tip extends within a combustion chamber of the engine. The center electrode is connected to an external electrical circuit at an outer terminal, whereas the side electrode is electrically connected through the metal shell to the engine block, which is electrically grounded. During engine operation, an electrical potential applied to the center electrode relative to the grounded side electrode generates a spark across the gap to ignite a fuel-air mixture within the combustion chamber.
It is believed engine performance may be affected by the orientation of the side electrode within the combustion chamber, for example, relative to an intake port or exhaust port. The optimum side electrode orientation may depend upon combustion chamber design and may vary even between combustion chambers of a multi-cylinder engine For a common spark plug that is threaded into a cylinder head bore and sealed against a seat therein, the orientation of the side electrode is random and uncontrolled. Thus, it has been necessary to employ costly and cumbersome techniques in order to achieve a desired side electrode orientation. For example, in racing engines or test engines, a desired orientation is achieved by an indexing technique which may involve trial of as many as a thousand commercial spark plugs to identify one spark plug wherein the random orientation of the side electrode corresponds to the desired orientation for the particular cylinder This also necessitates removal of the cylinder head to ascertain the orientation of the side electrode. Such techniques are too laborious, costly and time consuming for general use in automobiles.
It is an object of the present invention to provide an internal combustion engine comprising a spark plug assembly having a side electrode and installed in a cylinder head such that the side electrode is located in a predetermined orientation within the combustion chamber.
It is a more particular object of the present invention to provide an internal combustion engine comprising a spark plug assembly mounted in a bore of a cylinder head, which assembly comprises a side electrode received in a slot in the bore wall to achieve a predetermined orientation within the combustion chamber, and further comprises locking means for securing the spark plug assembly, including the side electrode, within the cylinder head. The locking means is threaded into the bore independent from the side electrode to permit the spark plug to be secured without altering the side electrode orientation.